1. Field of the Invention
The present invention relates to a plasma processing method used in the process of manufacturing semiconductor devices.
2. Description of the Related Art
When plasma etching is performed on an etching objective layer, a resist mask formed of, e.g., a photoresist is used. Particularly, in accordance with demands for micro-patterning, a photoresist frequently used in recent years is an ArF photoresist or F2 photoresist, i.e., a photoresist to be exposed to laser light from a light source of ArF gas or F2 gas, which is suitable for forming an opening pattern of about 0.13 μm or less.
However, since the ArF photoresist layer and F2 photoresist layer have a low plasma resistance, they cause a problem in that the surface of the photoresist layer becomes rough during etching. If the surface of the photoresist layer becomes rough, the shapes of opening portions are deformed with the etching progress, thereby making it difficult to obtain the designed shapes of etched holes or etched grooves. Furthermore, during etching, the photoresist disappears at some positions, and the etching proceeds to portions that are designed to be non-etched.
As a method of improving the plasma resistance of a photoresist layer, there is a method of irradiating the surface of a photoresist layer with ultraviolet rays, an electron beam, or an ion beam (Jpn. Pat. Appln. KOKAI Publication No. 60-110124, Jpn. Pat. Appln. KOKAI Publication No. 2-252233, and Jpn. Pat. Appln. KOKAI Publication No. 57-157523), a method of heat-setting a photoresist (Jpn. Pat. Appln. KOKAI Publication No. 4-23425), or a method of applying heat or light energy to an organic Si compound to coat the surface of a photoresist layer with a thin cured layer (Jpn. Pat. Appln. KOKAI Publication No. 2-40914).
In the above-described methods of improving the plasma resistance of a photoresist layer, it is necessary to perform a process of improving the plasma resistance in a container other than a container used in an etching step performed thereafter. Since a process subject to be processed needs to be transferred from the container for performing the process of improving the plasma resistance of a photoresist layer to the etching container, the yield is lowered in the transfer step and throughput is lowered due to a necessary transfer time. Furthermore, since the container for performing the process of improving the plasma resistance needs to be provided independently of the etching container, not only an additional space is required, but also the cost increases.
The etching container may be provided additionally with ultraviolet ray radiating means or heating means without independently disposing a container for performing the process of improving the plasma resistance. In this case, however, since the structure still requires the ultraviolet ray radiating means or heating means, the cost also increases.
On the other hand, where an etching objective portion is covered directly with a photoresist layer, the designed dimension accuracy of opening patterns is lowered in a step performed thereafter of performing exposure and development on the photoresist layer to form the opening patterns. For this reason, an antireflective layer is interposed between the etching objective portion and photoresist mask layer. It has been proposed to etch the antireflective layer with plasma of a gas containing a substance having C and F, such as a mixture gas of C4F8 and O2, a mixture gas of HBr, CF4, and He, or a mixture gas of CH2F2, CF4, and He (Jpn. Pat. Appln. KOKAI Publication No. 10-26162). It is also known to etch the antireflective layer with an etching gas, such as a mixture gas of CF4 and O2 (Jpn. Pat. Appln. KOKAI Publication No. 7-307328).
However, where the antireflective layer is etched with plasma of a mixture gas of C4F8 and O2, or a mixture gas of CF4 and O2, a problem arise such that the surface of the ArF photoresist layer becomes rough, a vertical stripe is formed in the ArF photoresist layer, or the ArF photoresist layer disposed as a mask layer is etched to a certain extent and thus hardly functions as a mask.